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modulated by Mn substitutionYoneda, Yasuhiro; Kohara, Shinji*; Noguchi, Yuji*; Miyayama, Masaru*
Transactions of the Materials Research Society of Japan, 40(1), p.29 - 32, 2015/03
Barium titanate (BaTiO) with a high dielectric constant is widely used in the production of ceramic capacitors. However, during sintering large numbers of ionized oxygen vacancies and conduction electrons are created. Doping with manganese is one of several ways to confine the electrons to a small region. In Mn-doped BaTiO there exist three valence states for the manganese ions, Mn
, Mn
, and Mn
. The Mn is nearly exactly incorporated into Ti sites and participates in the collective motion in the lattice. We performed local structure analysis by using atomic pair-distribution function (PDF) and X-ray absorption fine structure (XAFS). Figure 1 shows the obtained PDFs for pure BaTiO and 0.5%-Mn-doped BaTiO. All data collected at room temperature. Two obtained PDF patterns are well in agreement. Mn doping has hardly affected local structure.
Na)TiO
Matsuura, Masato*; Iida, Hiroyuki*; Hirota, Kazuma*; Owada, Kenji; Noguchi, Yuji*; Miyayama, Masaru*
Physical Review B, 87(6), p.064109_1 - 064109_10, 2013/02
Times Cited Count：30 Percentile：74.44(Materials Science, Multidisciplinary)Neutron-scattering studies of (BiNa)TiO (BNT) have been performed to elucidate the microscopic mechanism of the broad maximum in the temperature dependence of the dielectric constant at Tm 
600 K and the reduction in the piezoelectric properties above the depolarization temperature, 460 480 K. We observed diffuse scattering near the 
point below 700 K, which competes with the superlattice peak at the M point of the tetragonal phase but coexists with the superlattice peak at the R point of the rhombohedral phase. The diffuse scattering shows an anisotropic Q shape extending along the 
100
direction transverse to the scattering vector Q, which is explained by atomic shifts bridging the tetragonal and rhombohedral structures. We propose that the broad maximum in the dielectric constant is associated with a diffusive first-order transition between the competing tetragonal and rhombohedral phases. In addition, we found that the diffuse scattering is reduced for single crystals grown under high oxygen pressure, which suggests an analogy with the central peak in hydrogen-reduced SrTiO. Inelastic neutron scattering near the point reveals a heavily overdamped soft mode similar to those reported in lead-based relaxors, the "waterfall" feature. Moreover, a damped soft transverse acoustic mode is observed for the 100 direction as the anisotropic diffuse scattering, indicating phase instabilities with the same origin as that of the diffuse scattering. The recovery of the soft mode is observed near the depolarization temperature, which coincides with the disappearance of the superlattice peak at the M point. These results indicate that the depolarization and the waterfall feature originate in the dynamic nature of ferroelectric clusters in the coexisting tetragonal/rhombohedral phase.
crystalsYoneda, Yasuhiro; Kitanaka, Yuki*; Noguchi, Yuji*; Miyayama, Masaru*
Physical Review B, 86(18), p.184112_1 - 184112_11, 2012/11
Times Cited Count：60 Percentile：89.17(Materials Science, Multidisciplinary)The electronic structure of complex oxides is important for understanding their functional properties. Here we report the results of investigating multiferroic BiFeO using various X-ray spectroscopy techniques. Zn- and Mn-codoped and Mn-doped BiFeO samples were prepared with the aim of improving ferroelectric properties of BiFeO. The valences of the doped Mn and host Fe were investigated. When oxygen vacancies exist in the sample, Mn acts as a hole acceptor. Furthermore, Mn and Fe stabilize the perovskite unit by changing their ionic radius. As a result, Mn and Fe atoms exhibit various valence states in the BiFeO system. Evidence of the electronic structure for Fe 
-O 
-Bi 
hybridization is also presented.
)BiFeO-BaTiOOzaki, Tomoatsu*; Nishihara, Sadafumi*; Hosokoshi, Yuko*; Tokunaga, Masashi*; Noguchi, Yuji*; Miyayama, Masaru*; Yoshii, Kenji; Mori, Shigeo*
no journal, ,
We have investigated the local structure and physical properties of (1-)BiFeO-BaTiO. Electron-diffraction measurements showed the coexistence of magnetic and ferroelectric nano domains at around x=0.35. Dielectric measurements under magnetic field showed the lack of magneto-dielectric effect, indicating a weak correlation between the magnetic and ferroelectric properties. Magnetization-magnetic field curves showed the existence of magnetic nano domains.
Yoneda, Yasuhiro; Noguchi, Yuji*; Miyayama, Masaru*; Kitanaka, Yuki*
no journal, ,
BiFeO is not so large as intrinsic polarization is expected from a crystal structure since the coercive field is very large. However, good hysteresis is obtained by Mn-doping. In order to investigate the Mn dope effect of BiFeO, XAFS measurement was performed by each absorption edge of Bi, Fe, and Mn, and the estimate and local order structure of the valence were conducted. Since the valence and local structure of Mn are changing with annealing, they have suggested the importance of an oxygen deficiency.
